1. Field of the Invention
The present invention relates generally to a cell search method in a mobile communication system, and in particular, to a cell search method in a discontinuous reception mode in order to reduce power consumption in a mobile terminal.
2. Description of the Related Art
In general, mobility and portability are main characteristics of a mobile terminal. To ensure the mobility and portability, a battery is used as a power source for the mobile terminal. Waiting time is a period of time where components are in a low power consumption mode. Studies have been conducted to increase the waiting time in the mobile terminal.
Most of power consumption in a mobile terminal occurs due to sleep current, digital components, and radio frequency (RF) components in the mobile terminal. In order to increase the waiting time, power consumption in each element must be minimized. Sleep current refers to power consumption in a non-message reception period. Power consumption due to the sleep current is usually observed in an RF oscillator, an LCD (Liquid Crystal Display), a microprocessor, and power supplies. The RF oscillator experiences the highest sleep current power consumption. Therefore, power consumption in an RF oscillator must be reduced. To do so, it is necessary to reduce the time required to turn on an RF module.
A UMTS (Universal Mobile Telecommunication System) mobile terminal turns on an RF module periodically to check whether it has been paged. Specifically, the UMTS mobile terminal turns on a receiver periodically to monitor a PICH (Paging Indication Channel), detects a PI (Paging Indicator) from the PICH, and demodulates a PCH (Paging Channel) if PI=1 or PI=eraser. At the same time, the mobile terminal searches cells to determine whether there is a Node B having a higher signal strength than the current active set Node B. The cell search is usually performed in three steps, that is, slot timing synchronization, frame grouping, and a cell search.
According to the UMTS specification, a sliding PICH is used for a cell search. This is a method of buffering data while varying the turn-on time of the receiver and searching cells based on the buffered data.
However, the sliding PICH cell search method is not feasible in reality because a long time is required to collect frames of information needed for a cell search and the movement of the mobile terminal may change a radio environment during the time period.